title: Temporal and spectral characterization of the photosynthetic reaction center from Heliobacterium modesticaldum.
abstract: A time-resolved spectroscopic study of the isolated photosynthetic reaction center (RC) from Heliobacterium modesticaldum reveals that thermal equilibration of light excitation among the antenna pigments followed by trapping of excitation and the formation of the charge-separated state P800 (+)A0 (-) occurs within ~25 ps. This time scale is similar to that reported for plant and cyanobacterial photosystem I (PS I) complexes. Subsequent electron transfer from the primary electron acceptor A0 occurs with a lifetime of ~600 ps, suggesting that the RC of H. modesticaldum is functionally similar to that of Heliobacillus mobilis and Heliobacterium chlorum. The (A0 (-) - A0) and (P800 (+) - P800) absorption difference spectra imply that an 8(1)-OH-Chl a F molecule serves as the primary electron acceptor and occupies the position analogous to ec3 (A0) in PS I, while a monomeric BChl g pigment occupies the position analogous to ec2 (accessory Chl). The presence of an intense photobleaching band at 790 nm in the (A0 (-) - A0) spectrum suggests that the excitonic coupling between the monomeric accessory BChl g and the 8(1)-OH-Chl a F in the heliobacterial RC is significantly stronger than the excitonic coupling between the equivalent pigments in PS I.
authors.affiliation: Department of Physics, Purdue University, 525 Northwestern Ave, West Lafayette, IN 47907, USA.
authors.forename: Adrien
authors.initials: A
authors.lastname: Chauvet
authors.forename: Josephine
authors.initials: J
authors.lastname: Sarrou
authors.forename: Su
authors.initials: S
authors.lastname: Lin
authors.forename: Steven P
authors.initials: SP
authors.lastname: Romberger
authors.forename: John H
authors.initials: JH
authors.lastname: Golbeck
authors.forename: Sergei
authors.initials: S
authors.lastname: Savikhin
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Redding
mesh_terms: D000042:Absorption; D003013:Clostridium / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004735:Energy Transfer; D008958:Models, Molecular; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D013057:Spectrum Analysis; D013997:Time Factors
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins